1. Field of the Invention
This invention relates to selective permeable membranes made from polyquinazolone-based polymers.
2. Description of the Prior Art
In general, the term "selective permeable membrane" designates those membranes which prevent specific components contained in a liquid mixture, such as a solution or emulsion, from passing therethrough, and these membranes are generally anisotropic membranes having a structure wherein a surface layer containing dense and fine pores, i.e., skin layer is supported by a porous layer.
Typical examples of such membranes are a reverse osmosis membrane and an ultrafiltration membrane. The reverse osmosis membrane is, as is well known in the art, able to separate water from an aqueous solution containing relatively low molecular weight compounds, as well as salts such as sodium chloride, and is used to desalt sea water and brine, treating waste water from industrial plants and in purifying sewage. The ultrafiltration membrane, on the other hand, is capable of separating, from a solution or dispersion containing substances of large particle size, such as colloids, proteins, microorganisms, etc., and high polymeric substances, the solvent or dispersing agent used in the solution or dispersion, and is, therefore, used in the purification and concentration steps involved in the manufacture of foods and medicines, as well as in the brewing and fermentation industries.
Heretofore, as a material for preparing a selective permeable membrane of the above type, cellulose acetate has typically been used. This cellulose acetate membrane, when used as a reverse osmosis membrane for aqueous solutions, is excellent in its water permeation rate and efficiency of preventing specific solutes from passing therethrough, but is not completely satisfactory in heat resistance, pH resistance, chemical resistance, bacteria resistance, etc.
In order to overcome the above problems of the cellulose acetate membrane, selective permeable membranes made from polymers such as polysulfone, aromatic polyamide, polyimide, polyamidoimide, polyamidohydrazide, etc. have been proposed. With these selective permeable membranes, the above problems are solved to a certain extent, but they suffer from other disadvantages, such as that they are significantly inferior in permeation characteristics compared to the cellulose acetate membrane and that they are insufficient in chlorine resistance.
For example, an ultrafiltration membrane made from polysulfone is excellent in pH resistance and heat resistance, but shows very poor resistance to organic solvents. Further, the polysulfone is too hydrophobic so that it is difficult to form a reverse osmosis membrane. Selective permeable membranes made from aromatic polyamide, polyamidoimide, and polyamidohydrazide show improved pH resistance, bacteria resistance, etc., but are inferior in chlorine resistance and in general, they do not have sufficiently great permeability and are limited in practical usefullness. Furthermore, an aromatic polyimide membrane which has heretofore been proposed is not sufficient in alkali resistance and in general, not sufficient in permiability although it has excellent heat resistance. Additionally, for the production thereof, complicated and numerous steps are required. Thus, the aromatic polyimide membrane is of low practical value from the view point of both performance and cost.
Thus the heretofore proposed selective permeable membranes made from various polymers are, as described above, not entirely satisfactory in several respects.
Recently, a selective permeable membrane made from a polyquinazolone, in which quinazolone rings are connected by the carbon-carbon bond at the 2-position, -polyamide copolymer has been proposed as having excellent membrane characteristics. See Japanese Patent Application (OPI) No. 72777/1979 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). However, this membrane is a copolymer containing polyamide and is therefore not sufficient in chlorine resistance.